As disclosed in U.S. Pat. No. 4,347,381 (Tuvell), it is known that some tert-amines and derivatives thereof, e.g., amine oxides, betaines, and quaternary ammonium compounds, are subject to turning pink when exposed to acidic conditions. Neither the pink color body that is formed under acidic conditions nor its acid-activated precursor has yet been identified, and it is not known if the presence of the color body precursor as an impurity in some tert-amines is attributable to the raw materials and/or the techniques used in their syntheses. However, regardless of the primary reason for the discoloration, the pink coloration of the amines and their derivatives is undesirable because of its interference with dyes which are apt to be included in the formulations in which they are used.
A pink tert-amine or derivative thereof can have its color reduced in intensity or even removed by treating it with a bleaching agent, such as hydrogen peroxide, sodium sulfite, sodium bisulfite, sodium thiosulfate, or sodium hypochlorite, as in Tuvell; but it would be preferable to prevent the discoloration from occurring rather than to remove or reduce the discoloration later.
U.S. Pat. No. 3,922,306 (Takaku et al.) teaches that this discoloration of amine salts can sometimes be prevented when the amines are reacted with 0.01-5% by weight of certain borohydrides. According to Takaku et al., the effectiveness of the borohydrides in this regard is unexpected and unique, since it cannot be attained by the use of other reducing agents, such as the sodium sulfite or bisulfite, hydrazine, or hypophosphorous acid of their comparative example. However, it would be desirable to find an alternative to the borohydrides as agents for preventing discoloration of tert-amines and derivatives. As indicated by Tuvell, the borohydrides are too expensive to make their use commercially attractive.